class_docstr: Runs an op when a metric has plateaued.
code: def before_run(self, run_context):
      del run_context
  
      fetches = [self._global_step_tensor]
      if self._should_run_op and self.keep_alive:
          fetches.append(self._plateau_op)
          self._should_run_op = False
          self._ever_ran = True
  
      return tf.train.SessionRunArgs(fetches)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import tensorflow.compat.v1
  from tensorboard.backend.event_processing import event_accumulator
  from tensorboard.backend.event_processing import event_multiplexer
label_desc: Use image node_id 3 for calling the PlateauOpHook obj's underlying member method code with example usage: obj.before_run(run_context) and returns: tf